The invention relates generally to physical vapor deposition (PVD) and chemical vapor deposition (CVD) TiN processes such as are used in the fabrication of semiconductor devices.
Titanium nitride (TiN) is used in the manufacture of semiconductor devices, particularly as a barrier layer between a semiconductor substrate and a conductive layer which forms an electrical contact. The TiN barrier prevents interdiffusion of dissimilar materials, such as silicon and aluminum. It also is a good chemical barrier to gas phase species, such as tungsten hexaflouride, used in tungsten deposition processes.
Various process techniques, including both PVD and CVD, are used to produce TiN barrier layers. In the case of PVD, one might typically use a plasma to sputter a titanium target in a nitrogen atmosphere. The sputtered titanium atoms combine with plasma excited nitrogen gas species molecules to form TiN on the surface of the substrate. Subsequent to depositing the TiN layer, a heating step is then used to produce a titanium silicide at the interface between the TiN layer and the silicon substrate to thereby form an ohmic contact. In the case of CVD, a metallo-organic titanium compound (i.e., a precursor) is used to form the TiN film. The precursor readily decomposes at relatively low temperatures to deposit a TiN film on the surface of the substrate. The CVD method typically yields good deposition rates and excellent conformality and step coverage as compared to the PVD methods.
In general, however, regardless of the technique that is used, the quality of the CVD TiN film often leaves room for improvement. For example, it has been difficult to obtain TiN films that have sufficiently good electrical and physical characteristics. Often the resistivities of the CVD TiN films are not as low as desired. Thus, the process window for producing the film becomes is very small and the deposited films are very sensitive to small changes in process parameters. In addition, the CVD TiN films often tend to be unstable and their resistivity increases over time to such an extent that they are unusable as ohmic contacts.
Thus, further improvements in the techniques for producing high quality, stabile TiN films are still needed.